For businesses considering our dedicated server options, one of the questions you’ll need to answer about your server configuration is whether to utilize a RAID disk configuration or not. For our shared hosting customers, all of our shared server hardware utilizes a RAID disk configuration as a measure to help ensure maximum server uptime. With a single hard disk, you cannot prevent a significant downtime against a disk failure, which includes:
- The time required to obtain and install a replacement disk
- Reinstall the operating system
- Restore files from backup locations and
- Restore all the data entry performed since the last backup was made.
With multiple disks and a suitable redundancy scheme, your system can stay up and running when a disk fails, and even while the replacement disk is being installed and its data restored.
An Overview of RAID
RAID stands for Redundant Array of Independent Disks. The purpose of RAID is to provide redundancy for hard drives in the event that a hard drive is lost due to mechanical failure. Hard drives are the most susceptible component in a server to fail, just by the nature of it’s design.
RAID solves this problem by copying data from one drive to another in real time. For every bit that is written to one drive, it’s also written to it’s “mirror” counterpart. So, in the event that one drive is lost, the other drive is available to continue reading and writing data without any interruption to the server.
RAID 0 (Striped Disk Array without Fault Tolerance)
A non-redundant disk array, or RAID level 0, has the lowest cost of any RAID organization because it does not employ redundancy at all. This scheme offers the best performance since it never needs to update redundant information. Surprisingly, it does not have the best performance. Redundancy schemes that duplicate data, such as mirroring, can perform better on reads by selectively scheduling requests on the disk with the shortest expected seek and rotational delays. Without, redundancy, any single disk failure will result in data-loss. Non-redundant disk arrays are widely used in super-computing environments where performance and capacity, rather than reliability, are the primary concerns.
- Does not provide fault tolerance
- Minimum number of disks required = 2
- Usable storage capacity = 100%
- This is the fastest of the RAID configurations from a read-write standpoint
- Is the least expensive RAID solution because there is no duplicate data
- Recommended use for temporary data only
RAID 1 (Mirroring)
The traditional solution, called mirroring or shadowing, uses twice as many disks as a non-redundant disk array. Whenever data is written to a disk the same data is also written to a redundant disk, so that there are always two copies of the information. When data is read, it can be retrieved from the disk with the shorter queuing, seek and rotational delays. If a disk fails, the other copy is used to service requests. Mirroring is frequently used in database applications where availability and transaction time are more important than storage efficiency.
- Fault tolerant – you can lose multiple disks as long as a mirrored pair is not lost
- Minimum number of disks required = 2
- Usable storage capacity = 50%
- Good read performance, relatively slow write performance
- Recommended for operating system log files
RAID 5 (Block Interleaved Distributed Parity)
Consists of three or more hard drives. RAID 5 requires a minimum of at least three (3) drives. Redundancy is provided by “striping the parity” across all drives. This means that any one drive contains the “redundant” information. If one drive is lost, the other two drives continue reading and writing data without any interruption to the server.
- Fault tolerant – can afford to lose one disk only
- Minimum number of disks required = 3
- Usable storage capacity = subtract 1 whole disk from the total number in the array (i.e. 3 60Gig hard drives would provide 120Gig of usable disk space)
- Generally good performance, and increases with concurrency – the more drives in the array the faster the performance
- Recommended for operating system files, shared data, and application files
RAID 10 (A Stripe of Mirrors)
RAID 10 uses more disk space to provide redundant data than RAID 5. However, it also provides a performance advantage by reading from all disks in parallel while eliminating the write penalty of RAID 5. RAID 10 requires a minimum of at least four (4) drives In addition; RAID 10 gives better performance than RAID 5 while a failed drive remains unreplaced. RAID 10 offers faster data reads and writes than RAID 5 because it does not need to manage parity. Under RAID 5, each attempted read of the failed drive can be performed only by reading all of the other disks. On RAID 10, a failed disk can be recovered by a single read of its mirrored pair.
- Fault tolerant – you can lose multiple disks as long as both are not part of a mirrored pair
- Minimum number of disks required = 4
- Usable storage capacity = 50%
- Generally good performance, and increases with concurrency – the more drives in the array the faster the performance
- Recommended for operating systems, shared data, application files, and log files
We would recommend RAID 10 to all dedicated server owners for performance, uptime and disk redundancy. You do lose 50% of the total cumulative disk capacity, but the performance, redundancy and security of data makes up for it.
To know more about our RAID Hosting services and how your business would benefit from it, visit our RAID Hosting Services page.
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